The present application relates to a switched mode power supply with improved over temperature detection.
In order to protect power switching devices in switching power converters from overheating, temperature sensors are provided as close as possible to the power switches. As power devices have been reduced in size, they are more commonly mounted directly on the printed circuit board (PCB) surface. Thus, the temperature sensors are typically provided on the electrodes of the switch, since the thermal resistance in the copper traces is better than that of the PCB bulk material. However, when such sensors are attached to the electrodes, a large common mode noise results in the terminals of the temperature sensor as a result of the switching of the switches.
The block diagram of FIG. 1 illustrates one conventional approach to providing over temperature sensing for a switched mode power converter. FIG. 1 illustrates a temperature sensor 10, a noise generator 12 and the prior art temperature detector circuit 14 which includes a low pass filter 14a and a comparator 14b. The noise generator 12 triggers transient noise for each noise triggering event, typically based on switching activity of the power switches. The temperature sensor 10 produces a sensor signal which is disturbed by the switching noise and passed to the over temperature detector circuit 14. An over temperature alarm signal is provided as the output of the comparator 14b when the sensor output indicates an abnormally high temperature. In FIG. 1, the temperature sensor signal includes noise generated by the switching of the switches which may lead to an unreliable alarm signal from the temperature detector 14.
Thus, it would be advantageous to provide a temperature detector that avoids these problems.